The present invention relates to the absorption of carbon dioxide from gas streams. More particularly, it relates to the absorption of carbon dioxide gas from closed atmospheres to maintain healthful and safe conditions for humans and animals which breathe such atmospheres. Still more particularly, the present invention relates to the maintenance of breathable atmospheric conditions in closed or partially closed environmental contexts, including for example, space vehicles, submarines, underwater recirculating breathing apparatus, and closed circuit breathing apparatus used in hazardous conditions, such as fire fighting, as gas-masks and the like, by the absorption of exhalations of carbon dioxide. It also relates to a novel and surprisingly effective absorptive medium for the absorption of carbon dioxide, reduction of heat, reduction of water vapor and to the method of the use of such medium to absorb carbon dioxide from gas streams.
The present invention further relates to absorption medium which is operative over a wide variety of conditions, which is readily and safely utilizable and handleable in closed environments.
Methods and materials for removing carbon dioxide from confined breathing atmospheres such as found in submarines and spacecraft have been known for some time. Representative of such techniques is the use of activated carbon, specially formed sodium aluminum silicate compounds and alkali hydroxides. However, such prior art methods suffer from a number of disadvantages and limitations.
For example, activated carbon has relatively low absorption capacity at low pressures (below 50 psig) and its absorption capacity increases as temperature decreases requiring precooling of the bed before adsorption as well as the continuous precooling of the inlet feed gas mixture containing the CO.sub.2 to be removed.
Sodium aluminum silicate compounds have high affinity for water vapor which reduces the overall CO.sub.2 absorption capacity.
Alkali hydroxides are subject to moisture attack with subsequent caking, thus severely limiting capacity. Considerable levels of alkali dust become entrained in the air flow as well, posing a considerable hazard to the user. In addition, the use of solid alkali hydroxides results in the evolution of considerable amounts of heat which are awkward to deal with at best.
The prior methods and structures used for the removal of carbon dioxide from an atmosphere have also involved the use of washing the carbon dioxide containing atmosphere with caustic solutions which would result in the formation of metallic carbonates. Such solutions are quite easily made, relatively inexpensive and efficient in operation. These systems are quite inexpensive to operate and the metallic carbonates formed usually were consumed in by-product uses or simply discarded as waste.
Where availability or reagents, energy sources and space in which to carry on the treatment of carbon dioxide containing atmospheres are not limited for practical purposes, conventional systems have proved satisfactory. The problem facing the art is that of removing by-products of respiration such as carbon dioxide and water vapor (to prevent fogging, e.g. of the face mask lens) by such means that the minimum of space and weight is taken up with a minimum heat output.